The only current page I found for this device is this Chinese one, which didn't clarify anything. It looks like she's digitizing a blueprint.
That is the D-Mac Cartographic Digitiser, seen here in the 1968 Design journal (Issue 234):
It seems the D-Mac Cartographic Digitiser was developed from an earlier device called the D-Mac Pencil Follower, shown here in the 1968 Design journal:
Both devices appear to be early types of graphics tablet.